Layer system and blade

ABSTRACT

A layer system having a metallic substrate, in particular made of a &gt;=9% by weight chromium steel, in particular with roughness of the substrate &lt;=2 μm and optionally an intervening chromium layer directly on the substrate, in particular made of Cr/CrN, an underlayer or middle layer of AlCr, and an outer layer, in particular outermost layer, of AlCrO, where the AlCr and AlCrO layers in particular are PVD coatings wherein a shark skin effect is achieved with a simple geometric arrangement, and can be used particularly for compressor blades.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2018/077458 filed 9 Oct. 2018, and claims the benefit thereof.The International Application claims the benefit of German ApplicationNo. DE 10 2017 219 642.4 filed 6 Nov. 2017. All of the applications areincorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a layer system and a blade.

BACKGROUND OF INVENTION

Coatings for compressor blades must provide protection from oxidationand erosion.

Coatings considered are frequently only those that improve surfaceproperties.

SUMMARY OF INVENTION

The object of the invention is therefore to solve this problem.

The object is achieved via a layer system as claimed and a blade asclaimed.

The dependent claims list other advantageous measures which can becombined as desired with one another in order to achieve furtheradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the structure of the sharkskin,

FIG. 2 shows a lotus-flower surface,

FIG. 3 shows a layer system and

FIG. 4 shows an example of a turbine blade with possible uses.

DETAILED DESCRIPTION OF INVENTION

Current practice does not introduce surface structuring, becauseintroduction of this in known coatings has been complicated.

It is advantageous that the structure of an outer layer produces asharkskin effect. It advantageously comprises a PVD layer and/or acorrespondingly hard coating.

Known coatings for compressor blades, for example layers of lacquertype, applied via liquid mixtures, generally cannot achieve this effect.

A typical advantageous PVD coating is based on aluminum-chromium and/oraluminum chromium oxide. Further underlayers can be used for appropriatemodification of coefficients of thermal expansion or of protectivefunctions.

In an advantageous embodiment, an intervening chromium layer made ofchromium and of chromium nitride is applied on a substrate, surroundedby an aluminum-chromium-based base layer and an outeraluminum-chromium-oxide coating.

The figures and the description merely provide working examples of theinvention.

FIG. 1 shows a cross section through a triangular linear feature 11 of alayer 1 as an advantageous example of an elevation having triangularcross section.

The layer 3 has a minimum thickness h2, extending from which there is alinear feature 11 with height h1 having triangular cross section. Aplurality of these triangular linear features 11 are present, and thedistance between the peaks of the triangular linear features 11 is s.

The minimum thickness of residual thickness of the layer forming thebasis for the linear feature 11 is h2.

It is advantageous that the triangular linear features 11 constitute anisosceles triangle with an angle α.

The distance s is advantageously at least 2*maximum of h1, h2, and anadvantageous angle α is between 30° and 60°.

This structure is advantageously present only in the layer 3′ and inparticular entirely therein, i.e. without affecting and/or exposing asubstrate 4.

In the case of a layer comprising two or more sublayers, it isadvantageous that the structure is present only in the outermost coating3′ and does not expose the layer situated thereunder.

It is advantageous that the height h1≥4 μm and that the height h2≥2 μm,the intention here being that h2≥2*h1.

This type of structure can be applied to a compressor blade 20 (FIG. 4),where the main area of interest is advantageously in the front regionaround the upstream edge (22), with the aim of reducing turbulence andincreasing the efficiency level of the compressor.

Graduated structuring of a PVD layer on compressor blade surfaces as inFIG. 4 is also proposed. The surface structuring here is advantageouslyachieved in a single operation by means of laser beam interferenceprocessing (LBIP). In LBIP technology a laser beam is divided into twoor more laser beams and then transmitted onward to the workpiecesurface. The intensity of the laser undergoes periodic modulation here,and this permits structuring of the component surfaces. In the frontregion of the compressor blade (ingoing edge) two interfering laserbeams are superimposed to generate a microstructure for reduction offlow resistance (similar to sharkskin).

In the rear region of the compressor blade 20, LBIP technology is usedto create a surface structure that brings about what is known as“dewetting”. This greatly restricts water droplet formation on surfaces.The structuring of the surface reduces the risk of droplet formation anddroplet release, thus reducing expected erosion due to droplet impact.

The transition of the surface structuring from “sharkskin” to “dewettingeffect” here takes place in graduated fashion across the surface of thecompressor blade, with displacement of the transition region from thefirst stage to the final stage of the compressor, in the direction ofthe upstream edge.

This type of coating can advantageously be applied or produced acrossthe entire blade vane 23.

FIG. 2 shows a layer 3″ with a surface 2″ with lotus-flower effect.

There are many cones 33, in particular truncated cones advantageouslyarranged to form a grid. A cone 33 has triangular cross section.

Description of the cones 33 in respect of the height h1, the height h2and the arrangement in the layer 3″ is comparable with that of thelinear features 11′, 11″.

The cones 33 are configured entirely within the layer 3″.

FIG. 3 shows a layer system 46 made of hard layer 40 and soft layer 43.

The triangular elevations 11′, 11″, . . . ; 33, . . . are configuredonly in the hard layer 40, in particular in ceramic layers, for examplein particular AlCrO; said hard layer is also the outermost layer.

The layer 40 is configured to be at least 10% harder than the soft layer43.

The second layer is in particular metallic, very particularly made ofAlCr.

Directly on the substrate 41 there is advantageously a cathodicprotective layer 49 present which advantageously comprises an aluminumalloy or aluminum-chromium alloy.

The substrate 4, 41 is advantageously metallic, in particular made ofa >=9% by weight chromium steel, and in particular has roughness <=2 μm.

FIG. 4 shows by way of example a compressor blade 20 with a blade root28, and with a blade vane 23 with an upstream edge 22 and two differentsurface structures 24, 26.

In the upstream region around the upstream edge 22, the sharkskinalready described as per FIG. 1 is present on suction side and pressureside.

About halfway along the blade vane length, viewed in the direction offlow, the structure on suction side and pressure side changes withproduction of a lotus-flower-effect coating which, as depicted by way ofexample in FIG. 2, comprises projecting structures in the form of cones.

Such structures can be introduced subsequently by means oflaser-beam-interference treatment.

It is advantageous that a PVD layer provides the basis for the layer 7;3′, 3″. It primarily comprises an AlCr as basis-forming layer and anexternally located and overlying layer, in particular made of AlCrO.

The substrate 4 is advantageously chromium steel with at least 9% ofchromium (Cr), in particular with roughness <=2 μm.

The PVD coating has the following layer structure: —Cr interlayer (madeof Cr/CrN), —AlCr layer, —AlCrO layer as outer layer which thencomprises the linear features 11′, 11″ or cones 33.

1-14. (canceled)
 15. A layer system, at least comprising: a metallicsubstrate, and optionally an intervening chromium layer directly on thesubstrate, an underlayer or a middle layer comprising AlCr, and an outerlayer, comprising AlCrO.
 16. The layer system as claimed in claim 15,further comprising: a surface on the outer layer comprising a pluralityof elevations having triangular cross section.
 17. The layer system asclaimed in claim 16, wherein the surface on the outer layer comprises,as triangular elevations, triangular linear features, and/or straightlinear features.
 18. The layer system as claimed in claim 17, wherein aheight of the triangular linear features is h1, where a distance betweentwo directly adjacent triangular linear features or the peaks of thetriangular linear features is s, and wherein a distance s≥2*h1.
 19. Thelayer system as claimed in claim 17, wherein the triangular linearfeatures are isosceles triangles and/or have a base angle (a) between30° and 60°.
 20. The layer system as claimed in claim 17, wherein thetriangular linear features run parallel to one another, or wherein allof the triangular linear features run parallel to one another.
 21. Thelayer system as claimed in claim 16, wherein the surface on the outerlayer comprises cones as triangular elevations.
 22. The layer system asclaimed in claim 21, where a height of the cones is h1, where a distancebetween two directly adjacent cones or the peaks of the cones is s, andwhere a distance s≥2*h1.
 23. The layer system as claimed in claim 21,wherein the cones are arranged to form a grid.
 24. The layer system asclaimed in claim 16, wherein the elevations having triangular crosssection are configured only in one layer, or in one outermost layer, orentirely in one layer.
 25. The layer system as claimed in claim 24,wherein the layer system is configured to have two or three sublayers,wherein a surface on the outer layer comprises a plurality of elevationshaving triangular cross section, where the outer layer forms anoutermost layer.
 26. The layer system as claimed in claim 15, wherein athickness of the intervening chromium layer is 0.2 μm.
 27. The layersystem as claimed in claim 15, wherein the metallic substrate is made ofa >=9% by weight chromium steel.
 28. The layer system as claimed inclaim 15, wherein the metallic substrate has a roughness of <=2 μm. 29.The layer system as claimed in claim 15, wherein the interveningchromium layer is made of Cr/CrN.
 30. The layer system as claimed inclaim 15, wherein the underlayer or middle layer consists of AlCr. 31.The layer system as claimed in claim 15, wherein the outer layercomprises an outermost layer.
 32. The layer system as claimed in claim15, wherein the outer layer consists of AlCrO.
 33. The layer system asclaimed in claim 15, wherein the AlCr and AlCrO layers are PVD coatings.34. A blade, or a compressor blade, comprising: at least to some extent,or entirely, a layer system as claimed in claim
 15. 35. The blade asclaimed in claim 34, further comprising: a surface on the outer layerwhich comprises a plurality of elevations having triangular crosssection when viewed in a direction of flow around an upstream edge, on asuction side and a pressure side, and wherein the surface on the outerlayer comprises cones as triangular elevations from halfway onward inthe direction of flow around a blade vane, on the suction side and thepressure side.